1. Field of the Invention
The present invention relates generally to methods for controlling incoming or received electronic mail (email). More specifically, the invention relates to methods for protecting against the receipt of unwanted or “spam” email in a telecommunication system.
2. Description of the Related Art
Email is becoming a crucial tool of daily life. However, a recent upswing in the amount of “spam”, i.e. email broadcast advertisements, has caused both considerable congestion on the internet and great concern to internet users, particularly in light of how inexpensive and efficient spamming techniques have become and the ease with which spammers have been able to avoid having their outgoing email traffic filtered out by the intended recipients. The act of sending “junk email”, i.e. the mass mailing of unsolicited email messages based on address lists collected from various sources to which receivers of email have supplied their addresses for other purposes, is called “spamming” and threatens to overwhelm the legitimate uses of email. Spammers avoid filtering by, for example, moving their originating locations from domain to domain or otherwise disguising themselves. Typically, the Standard Mail Transfer Protocol (SMTP) for internet email requires that all email messages contain a header that includes the sender's email address (a “source” address and/or “return” address) and the receiver's email address (a “destination” address). However, it is possible to give incorrect sender information and still have the email delivered. Therefore spammers can simply change the indicated source address and continue sending unwanted email if a certain receiver decides not to accept incoming email from a certain sender.
As more users rely on email for daily communication, classification of email has taken on added significance. Classification of email messages allows users to treat classes of email differently and the need for classification is growing due to the explosive growth of spamming techniques currently utilized and encountered. This explosive growth is undesirable and potentially dangerous since the reliance on email as a vital form of electronic communication has become so pervasive in society today that its interruption or misuse threatens to stymie all forms of business communication, health care provision, military exchange of information, and the like.
Attempts have been made to design email systems and protocols that will alleviate the problems introduced by and associated with spam email. For example, methods exist for categorizing email which allow unrequested email to be automatically erased without consuming any system resources or user time. However, the model of the spammer assumed by the methods of Gabber et al. is a rather cooperative spammer who is limited to acquiring email addresses of receivers of email by merely purchasing lists of email addresses or acquiring them from newsgroups and the like. Thus, should a spammer become more militant, i.e. devise new strategies of acquiring email addresses, it is likely that the methods taught by Gabber et al. will be ineffective to prevent spamming.
Other attempts to prevent unwanted email include filtering the email according to the sender's address and according to recognized message and subject keywords. However, this is inefficient and easily thwarted by adversaries who intentionally avoid particular keywords that are known to be blacklisted, and/or who camouflage certain blacklisted source addresses or domains. Another currently-employed solution is to use electronic mail channel identifiers wherein a receiver assigns a different channel to each known sender by giving each of them a unique email address at which to contact the receiver. In this scheme, incoming mail gets sorted or rejected according to the address to which it is sent and the sender from which they originate. Other related attempts to prevent spamming have also been employed, but all of these approaches fail to effectively prevent the militant spammer from sending junk email that reaches an intended recipient's in box.
As internet technologies become more sophisticated over time, so will the efforts and knowledge of spammers desiring to send their messages indiscriminately through all of cyberspace. It is envisioned that spammers will soon have the ability to control the communication media of interest and be capable of corrupting large numbers of email protocol participants. This will allow such abusers of email systems to corrupt the email systems with abandon for their own selfish motives, and to the general detriment of all users of the systems. It would be desirable if these untoward results could be avoided.
Accordingly, there is a long-felt, but unresolved, need in the art for methods of preventing militant spammers from corrupting email systems with unwanted, junk email. These methods should be versatile and easy to implement in current email systems. Furthermore, it would be desirable if these methods shifted the computational and bulk storage requirements of implementing such methods back onto the spammer so as to alleviate for the potential receiver of the spam email the expense of fighting off unwanted spam attacks. Such results have not heretofore been achieved in the art.